Innovative tracers for subsurface characterization

Proper site characterization is a critical component in making risk-based decisions and in selecting an appropriate action for a site, whether it is active remediation, containment or natural attenuation. The overall purpose of this work is to investigate innovative techniques for characterizing the factors controlling the transport and fate of organic chemicals at contaminated sites. It is expected that results from this work will lead to improved and more cost-effective methods for characterizing contamination at hazardous waste sites. The information gained from using these methods may lead to a better understanding of factors controlling contaminant transport at sites and therefore more informed risk-based decision making and selection of remediation strategies. The results indicate that (1) the presence of porous media heterogeneity and distinct zones of dense nonaqueous liquid (DNAPL) saturation lead to reduced performance (reduced accuracy) of the partitioning tracer test for measuring DNAPL saturation in saturated subsurface systems, (2) gas-phase tracer tests have the potential to accurately measure water contents for a system with uniform water content and homogeneous porous media, (3) the diffusivity-tracer test method can be used to determine whether diffusion-mediated processes are significant at a particular site, and (4) for a 2-dimensional flow cell flushing experiment the magnitude of trichloroethene concentration and the shape of the trichloroethene elution curves varied as a function of location and sampling type and that the less than solubility concentrations observed at almost all ports were caused by the nonuniform NAPL distribution and porous media heterogeneity, rather than by rate-limited interphase mass transfer at the pore-scale